Hill S A
Department of Biological Sciences, Northern Illinois University, DeKalb 60115, USA.
Mol Gen Genet. 2000 Oct;264(3):268-75. doi: 10.1007/s004380000316.
Neisseria gonorrhoeae lacks several common DNA repair pathways found in other organisms. As recent evidence had indicated that gonococci use recombinational repair to repair UV-induced DNA lesions, this study examined whether the gonococcal RecJ homologue contributes in this repair capacity. The recJ gene from strain MS11 was cloned and sequenced and was found to show a considerable degree of identity to its Escherichia coli homologue. A N. gonorrhoeae delta recJ mutant was constructed and tested for recombinational proficiency as well as for defects in DNA repair. In the absence of the RecJ exonuclease, DNA transformation and pilin switching occurred at wild type levels, indicating that the efficiency of recombination remained unimpaired. In contrast, N. gonorrhoeae delta recJ mutants showed extreme sensitivity to low levels of UV irradiation and to exposure to DNA-alkylating reagents [e.g. ethyl methanesulfonate (EMS) and methyl methanesulfonate (MMS)]. Complementation of the gonococcal recJ mutant in cis restored resistance to low-level UV, indicating that the gonococcal RecJ protein is involved in recombinational repair, and can act independently of other single-strand-specific exonucleases. Furthermore, transformation competence was not required for RecJ-dependent DNA repair. Overall, the data show that N. gonorrhoeae recJ mutants present a unique phenotype when compared to their E. coli recJ counterparts, and further support the contention that RecORJ-dependent recombinational repair is a major DNA repair pathway in the genus Neisseria.
淋病奈瑟菌缺乏其他生物体中常见的几种DNA修复途径。由于最近的证据表明淋球菌利用重组修复来修复紫外线诱导的DNA损伤，本研究检测了淋球菌RecJ同源物是否有助于这种修复能力。对菌株MS11的recJ基因进行了克隆和测序，发现它与其大肠杆菌同源物有相当程度的同一性。构建了淋病奈瑟菌recJ缺失突变体，并检测其重组能力以及DNA修复缺陷。在没有RecJ核酸外切酶的情况下，DNA转化和菌毛蛋白转换在野生型水平发生，这表明重组效率未受损害。相比之下，淋病奈瑟菌recJ缺失突变体对低水平紫外线照射和暴露于DNA烷化剂[如甲磺酸乙酯（EMS）和甲磺酸甲酯（MMS）]表现出极端敏感性。淋病奈瑟菌recJ突变体的顺式互补恢复了对低水平紫外线的抗性，这表明淋病奈瑟菌RecJ蛋白参与重组修复，并且可以独立于其他单链特异性核酸外切酶发挥作用。此外，RecJ依赖性DNA修复不需要转化能力。总体而言，数据表明，与大肠杆菌recJ对应物相比，淋病奈瑟菌recJ突变体呈现出独特的表型，并进一步支持了RecORJ依赖性重组修复是奈瑟菌属主要DNA修复途径的观点。
